Speaking of which, each mission mixes it up with a variety of objectives; destroy all the enemy [air/ground/sea] units, defend a specific [air/sea] unit...  actually, that's about it.  You will spend 99% of the time shooting at things on land, sea, or air.  The straight-up attack tasks are great, especially in the air.  As mentioned before, your death is a rare thing (unless you crash into the ground), so you can fly and shoot to your hearts content.  Ground and (especially) naval units are not as fun, but still a worthy diversion.  I found the unguided bombs particularly troublesome, because the default camera angle places your plane directly between you and the target, leaving guidance pretty much up to luck and guesswork.

The real headaches and smashed controllers come with the defense tasks.  The objects of your protection usually lose health extremely rapidly, requiring a multitude of restarts and herculean efforts to successfully defend.  I suspect it was designed this way to counterbalance the comparitively easy air-combat portions.  Thankfully there is a robust checkpoint system in place, which saves your progress after every major task.  It's not perfect, of course; more than once I had to restart a mission from the beginning because the checkpoint saved when the object I was defending had only a sliver of health left, creating a loop of near-instantaneous death and reload.

Despite my complaints, I found myself having a good time more often than not.  Most of the missions are essentially the same, making Heatseeker a game best enjoyed in small doses.  Multiplayer, whether on or offline, would extend the longevity.  In particular, a co-op mode would make certain missions considerably more enjoyable.  Still, if you're a fan of aerial combat (or suspect you might be), and you can live with less-than-stellar graphics and occasional periods of extreme frustration, Heatseeker just might keep you amused for a dozen hours or so.  At roughly half the price of most newly released titles, that's not a bad deal at all.